Femoral reference tibial cut guide

ABSTRACT

Illustrative embodiments of a femoral reference tibial cut guide are presented for cutting the proximal tibia to receive a tibial implant. The cut guide references the femur to determine the appropriate tibial

FIELD OF THE INVENTION

[0001] The present invention relates to a bone cutting guide, inparticular to a guide for cutting the proximal tibia which establishesthe tibial cut level by referencing the femur.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Various embodiments of the present invention will be discussedwith reference to the appended drawings. These drawings depict onlyillustrative embodiments of the invention and are not to be consideredlimiting of its scope.

[0003]FIG. 1 is an exploded oblique elevation view of an illustrativetibial cut guide assembly according to the present invention.

[0004]FIG. 2 is a top plan view of the tibial cut guide assembly of FIG.1.

[0005]FIG. 3 is an oblique elevation view of the tibial cut guideassembly of FIG. 1 positioned adjacent a knee joint in extension.

[0006]FIG. 4 is an oblique elevation view of the tibial cut guideassembly of FIG. 1 positioned adjacent a knee joint in flexion.

[0007]FIG. 5 is an exploded side elevation view of an alternativeillustrative embodiment of a depth reference probe.

[0008]FIG. 6 is a top plan view of the alternative depth reference probeof FIG. 5.

[0009]FIG. 7 is an oblique elevation view of the alternative depthreference probe mounted on the cut guide of FIG. 1 and positionedadjacent a knee joint in flexion.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0010] FIGS. 1-4 depict an illustrative tibial cut guide 2 assemblycomprising a base 4, a cut head 6, and a depth reference probe 8. Thebase 4 includes an elongate body 10 having a proximal end 12, a distalend 14, and a longitudinal axis extending from the proximal end to thedistal end. A pair of support arms 16 extends medially and laterallyfrom the proximal end generally perpendicular to the longitudinal axis.Fixation holes 18 extend through the base 4 at the proximal end 12. Alongitudinal bore 20 opens at the proximal end and extends along aportion of the longitudinal axis. A side opening 22 in the base 4includes a top surface 24 and bottom surface 26. The longitudinal bore20 extends through the top and bottom of the side opening 22 tocommunicate with the side opening 22.

[0011] The cut head 6 includes a body 30 having a proximal surface 32, adistal surface 34, an anterior side 36, a posterior side 38, a medialside 37, and a lateral side 39. A saw guide slot 40 extends through thecut head 6 from the anterior side 36 to the posterior side 38 to definea cutting plane having a downward posterior slope, typically on theorder of 7°. The proximal surface 32 is parallel to the slot and canalternatively be used as a saw guiding surface offset a known distancefrom the slot. A mounting hole 41 extends from the proximal surface 32down to communicate with the slot 40. Fixation holes 42 extend throughthe medial and lateral sides 37, 39 of the cut head body 30 directedfrom anterior to posterior. A threaded, elongate elevation shaft 44extends downwardly from the distal surface 34. An adjustment knob 46includes an elongate cylindrical body 48 having a proximal end 49, adistal end 50, and a threaded through bore 51. The body 48 of the knob46 is sized to fit within the side opening 22 with its through bore 51aligned with the base through bore 20 and its proximal 49 and distal 50ends adjacent the top 24 and bottom 26 surfaces of the side opening 22.The side of the knob 46 projects through the side opening 22 to provideaccess to turn the knob 46.

[0012] The cut head 6 is assembled to the base 4 by inserting theadjustment knob 46 into the side opening 22 and inserting the elevationshaft 44 into the longitudinal through bore 20. The adjustment knob isthen threaded onto the elevation shaft 44 to retain the cut head 6 inthe base 4. The cut head 6 is constrained against proximal-distal motionby the abutment of the proximal end 49 and distal end 50 of the knob 46with the top 24 and bottom 26 of the side opening 22. Proximal-distaladjustment of the cut head is accomplished by turning the knob 46 whichmoves the elevation shaft 44 relative to the knob.

[0013] A depth reference probe 8 includes a cylindrical body 60 having aproximal end 62, a distal end 64, and a longitudinal axis extending fromthe proximal end 62 to the distal end 64. A probe arm 66 extends fromthe body 60 adjacent the proximal end 62 generally perpendicular to thebody axis. The arm 66 terminates at an upturned probe tip 68. Anengagement tab 70 extends from the body 60 adjacent the distal end 64generally perpendicular to the body axis. The tab 70 is double ended,having a first end 72 spaced a first axial distance from the probe tip68 and a second end 74 spaced a second axial distance from the probe tip68 as measured along the longitudinal axis of the body 60. Each end ismarked with the tibial implant thickness required to restore the knee tothe spacing existing at the time the probe is used to position thetibial cut guide. The engagement tab 70 is mounted on the body 60 forrotation about the longitudinal axis so that the first and second ends72, 74 can be alternately positioned on the same side of the body as theprobe tip 68. The first and second ends 72, 74 of the engagement tab 70are sized to fit within the saw guide slot 40.

[0014]FIG. 3 shows the cut guide assembly in process of being mountedadjacent a knee joint including a femur 80 and a tibia 82. The base 4 ispositioned adjacent the proximal end 84 of the tibia 82 with the supportarms 16 in contact with the tibia and the longitudinal base axisparallel to the tibial bone axis. Fixation pins are inserted through thebase fixation holes 18 to anchor the base 4 in position. The knee isplaced in zero degrees of flexion and the bones are distracted to theextent permitted by the soft tissues surrounding the joint. Distractioncan be accomplished by using a retractor, by using traction, or by othersuitable means. The adjustment knob 46 is turned to move the cut headand probe tip 68 up until the tip 68 contacts the distal femoral bone.This sets the tibial resection level to a known distance from thefemoral bone.

[0015] Tibial implants are typically provided as one-piece or two-piececonstructs. The probe 8 is sized to correspond to the available totaltibial implant thicknesses so that when the tibia 82 is cut, the surgeonis assured that there is a tibial implant with a total thickness thatwill exactly replace the cut bone and reproduce the joint spacing andsoft tissue tension that existed at the time the probe adjustment wasmade. When the probe 8 is to be used with a femur 80 that has alreadybeen cut to receive a femoral implant, as shown in FIG. 2, the probespacing includes the thickness of the femoral implant as well as thethickness of the tibial implant. However, femoral implants are typicallydesigned to replace the same amount of bone regardless of size, so onlythe tibial implant thickness needs to be shown on the probe 8. When theprobe 8 is to be used with an uncut femur, the probe spacing correspondsto the thickness of the tibial implant. Each probe 8 can have twospacings that are alternatively selectable as shown in the illustrativeembodiment and multiple probes can be provided that correspond to avariety of possible implant thicknesses.

[0016] After the desired resection level is set, fixation pins areinserted through the cut head fixation holes 42 to fix the cut head 6 inposition. The probe 8 is removed and a saw blade is activated throughthe saw slot 40 to cut the proximal tibia 84 at the desired level. Thecut head 6 and base 4 are then removed and the implants inserted.

[0017] In addition to setting the resection level with the knee in zerodegrees of flexion, the tibial cut guide assembly can be used at otherflexion positions between zero degrees and full flexion. FIG. 4 showsthe illustrative cut guide assembly 2 mounted on the knee inapproximately ninety degrees of flexion. The resection level is set asdescribed above. Furthermore, after the resection level is set at oneangle of knee flexion, the knee can be repositioned and compared to thecut guide assembly to see if the same resection level will suffice forthe new position. If not, the soft tissues constraining the knee jointcan be selectively cut to balance the resection level at differentflexion angles. The resection level can also be adjusted to a compromiseposition.

[0018] FIGS. 5-7 show an alternative illustrative embodiment of a probe90. The probe 90 includes a threaded, elongate shaft 92 having aproximal end 94, a distal end 96, and a longitudinal axis from theproximal end 94 to the distal end 96. A cut guide engaging portion 98 isformed adjacent the distal end 96 and includes a bore 100 containing aspring 102 and a ball 104. Size indicia or marks 106 corresponding tothe available total tibial implant thicknesses are spaced along theshaft. A probe blade 108 includes a flat upper surface 110, a lowersurface 112, and a through hole 114 from the upper surface to the lowersurface. A knob 116 comprises a cylindrical body having a proximal end118, a distal end 120, and a longitudinal axis from the proximal end 118to the distal end 120. A threaded, axial through bore extends throughthe knob 116 from the proximal end 118 to the distal end 120. Theexterior of the knob 116 is threaded adjacent the distal end 120. Theexternally threaded portion of the knob fits through the hole 114 in theblade and is held in place by a nut 122 threaded onto the distal end ofthe knob 116. After tightening the nut 122, the knob 116 remainsrotatable relative to the blade 108. The knob 118 is threadably receivedon the shaft 92 such that by turning the knob relative to the shaft 92and blade 108, the blade 108 can be positioned up and down on the shaft.The implant thickness setting is read by noting which mark 106 isadjacent the nut 122.

[0019] In use, the probe 90 is mounted on the cut head 6 by insertingthe cut guide engaging portion 98 into the mounting hole 41 until theball 104 snaps into the slot 40 to retain the probe in place. Thelongitudinal axis of the probe shaft 92 will be perpendicular to theproximal surface 32 of the cut head and thus perpendicular to the slot40 of the illustrative embodiment. The blade is angled to compensate forthe posterior slope of the slot 40 and proximal surface 32 of the cuthead 6 such that the upper surface 110 of the blade 108 is approximatelyhorizontal when the tibia 82 is oriented vertically. The blade 108 isadjusted to a desired implant thickness setting by turning the probeknob 118 until the nut 122 is adjacent the desired mark 106.

[0020] With the base 4 of the cut guide assembly pinned to the tibia 82,the cut head 6 is adjusted up and down by turning the adjustment knob 46until the blade 108 contacts the femur. If it is desirable to removemore or less bone from the tibia 82, the knob 116 is turned to adjustthe blade up or down the shaft to the next mark 106 corresponding to atibial implant thickness and then the cut head 6 is repositioned. Theknee can be positioned in different degrees of flexion, such as zero andninety degrees, to set the tibial cut depth. The adjustability of theblade 108 of this embodiment also makes it possible to get a directreading in millimeters comparing the gap between the femur and tibia atdifferent flexion angles. For example, the guide can first be set withthe knee in full extension. After repositioning the knee to ninetydegrees of flexion, the knob 116 can be turned to reposition the blade108 against the bone. The difference in the flexion and extension gapsis shown by the difference between the marks 106 on the probe shaft 92that aligned with the blade in the two knee positions.

[0021] Where the femoral bone has already been cut, as shown in the FIG.7, the flat upper surface 110 of the blade facilitates positioning thefemur 80 at flexion angles corresponding to the femoral bone cuts. Forexample, in extension, the distal cut surface 130 will lie flat againstthe blade 108. In flexion, the posterior cut surface 132 will lie flatagainst the blade. The blade 108, can be narrow, as shown, to contactone femoral condyle or corresponding cut surface at a time.Alternatively, the blade can be wide so that both condyles contact theblade at the same time. Likewise, the cut guide described above can beused with a unicondylar knee arthroplasty as well as a total kneearthroplasty.

[0022] It will be understood by those skilled in the art that theforegoing has described illustrative embodiments of the presentinvention and that variations may be made to these embodiments withoutdeparting from the spirit and scope of the invention defined by theappended claims. For example the illustrative embodiments depict usingsaw guides and blades to make the bone cuts. However, the claimedmethods and cut guides could also be used with other bone removalsystems to set their reference bases to achieve the desired position ofthe tibial resection.

What is claimed is:
 1. A tibial cut guide for cutting the proximal tibiaof a knee joint, including a femur and a tibia, to prepare the joint forreceiving an implant, the tibial cut guide comprising: a cutter guide; aprobe connected to the cutter guide, the probe being sized to contactthe femur and space the cutter guide from the femur a predetermineddistance.
 2. The tibial cut guide of claim 1 wherein the probe is sizedto space the cutter guide from the femur a distance corresponding toavailable implant thicknesses.
 3. The tibial cut guide of claim 1further comprising a plurality of probes interchangeably connectable tothe cutter guide, each probe being sized to space the cutter guide fromthe femur a different distance corresponding to a different availableimplant thickness.
 4. The tibial cut guide of claim 1 wherein the probeincludes a reference surface and the probe is adjustable to position thereference surface at different known distances from the cutter guide. 5.The tibial cut guide of claim 4 wherein the probe includes indiciacorresponding to different available implant thicknesses and the probeis adjustable to position the reference surface relative to the indicia.6. The tibial cut guide of claim 1 wherein the cutter guide is a slotfor guiding a saw blade and the probe includes a reference surface forcontacting the femur, the probe engaging the slot to space the slot aknown distance from the reference surface.
 7. The tibial cut guide ofclaim 1 wherein the probe includes a planar reference surface that isable to engage a flat planar surface on the femur.
 8. The tibial cutguide of claim 7 wherein the reference surface is a planar surface. 9.The tibial cut guide of claim 8 wherein the reference surface is lessthan one-half the width of the femur.
 10. The tibial cut guide of claim9 wherein the reference surface is greater than one-half the width ofthe femur.
 11. The tibial cut guide of claim 1 further comprising a cutguide base, the cut guide base including means for fixing the cut guidebase to the tibia, the cutter guide being adjustably mounted on the cutguide base such that the cutter guide can be adjusted up and downrelative to the base, the probe further including a reference surfaceand a support having indicia on it, the reference surface beingadjustable up and down the support to position the reference surfaceadjacent each of the indicia.
 12. A method comprising the steps of:positioning a knee joint comprising a tibia and a femur in a desiredalignment and spacing; positioning a tibial cut guide adjacent to theproximal tibia, the tibial cut guide including a probe; contacting thefemur with the probe to space the tibial cut guide a known distance fromthe femur; and guiding a cutter with the tibial cut guide to cut thetibia at the level determined by contacting the femur.
 13. The method ofclaim 12 further including the step of removing the probe from thetibial cut guide before cutting the tibia.
 14. The method of claim 13further including the step of anchoring the tibial cut guide to thetibia before removing the probe.
 15. The method of claim 14 wherein theprobe spaces the tibial cut guide from the femur a distance correlatedto the available implant thicknesses, the method further including thesteps of: removing the cut guide after cutting the tibia; and replacingthe cut bone with a tibial implant having a thickness correlated withthe probe spacing.
 16. The method of claim 15 further comprising thesteps of: selecting the probe from a plurality of probes correspondingto different available implant thicknesses; and connecting the selectedprobe to the tibial cut guide before contacting the femur with theprobe.
 17. The method of claim 15 wherein the probe includes a referencesurface and the probe is adjustable to position the reference surface atdifferent known distances from the tibial cut guide and the step ofcontacting the femur with the probe comprises contacting the femur withthe reference surface.
 18. The method of claim 17 wherein the probeincludes indicia corresponding to different available implantthicknesses and the probe is adjustable to position the referencesurface relative to the indicia.
 19. The method of claim 12 furthercomprising the step of cutting the femur to receive a femoral implant;and wherein the step of contacting the femur with the probe comprisescontacting the cut surface of the femur with the probe.
 20. The methodof claim 19 wherein the reference surface is a planar surface and themethod further comprising the step of adjusting the flexion angle of theknee so that the cut surface of the femur is parallel with and incontact with the planar surface.
 21. The method of claim 12 wherein thestep of positioning the knee joint in a desired alignment and spacingincludes separating the femur and tibia with a retractor.
 22. The methodof claim 12 wherein the step of positioning the knee joint in a desiredalignment and spacing includes separating the femur and tibia usingtraction.
 23. A method comprising the steps of: positioning a knee jointcomprising a tibia and a femur at a first angle of flexion; positioninga tibial cut guide adjacent to the proximal tibia, the tibial cut guideincluding a probe, the probe including a reference surface and aplurality of indicia indicating a linear distance from the referencesurface to the tibial cut guide, the reference surface being adjustablebetween the plurality of indicia; contacting the femur with thereference surface in a first position; fixing the position of the tibialcut guide; noting which of the indicia corresponds to the referencesurface first position; repositioning the knee joint to a second angleof flexion; contacting the femur with the reference surface in a secondposition; noting which of the indicia corresponds to the referencesurface second position; and comparing the indicia corresponding to thereference surface first and second positions to determine the differencein the spacing between the femur and tibia in the two flexion positions.24. The method of claim 23 wherein the two flexion angles areapproximately 0° degrees of flexion and 90° of flexion.